Opponents of a state ballot question that would allow marijuana to be used for medical purposes are urging Massachusetts voters to reject the proposed law. They say it's poorly drafted and could be easily exploited.

Legislators and law enforcement officials were among those who spoke Monday at an event held by the Vote No on Question 3 Committee.

The ballot question would allow patients with conditions such as cancer, AIDS and glaucoma to register to obtain marijuana at 35 dispensaries in Massachusetts.

State Sen. John Keenan, a Quincy Democrat, said the measure was "vague, ambiguous and wide open for exploitation." Among other things, he said there would be too few safeguards to keep the drugs away from children.

Supporters say marijuana is a proven pain management tool for people with debilitating conditions.